The Mobile Terminated sending of the short messages (SMS-MT) is described in reference GSM (Global System Mobile) documents. It involves a 3 stage process:
a) From the Destination Address of the handset, use a look-up table (called HLR levels which gives the address of the Home Location Register (HLR) of this subscriber such as:
According to this example, the HLR address for the subscriber of Network A which has +85288712345 is immediately found to be +85288700001.
b) Send a request (Send Routing Info (SRI)) to this HLR to obtain the address of the visited MSC (Mobile Switch Centre).
c) Send a Forward Short Message Mobile Terminated (SMSMT) to the visited MSC which will relay to the Destination Address handset. In case of failure, various classical retry schemes may be used.
However this process must be adapted, according to the invention for certain cases.
Several countries such as Netherlands, Hong-Kong, United Kingdom and many other in the future have implemented the Mobile Number Portability (MNP) feature. In order to develop the competition between the mobile operators, the MNP allows a subscriber to keep the same number even if he changes to an other Mobile network of the same country (MNP country).
As a result, it is not possible to know, from the handset number, which network it belongs and which precise HLR to interrogate. In the above example, a handset +85288712345 could belong to network C if it has been port-out from network A to network C.
Case of Incompletely Known HLR Levels with SMS Interworking.
For large networks, the number of HLR levels could be several hundred intervals (around 1000 for the largest, such as France Telecom) because of the number of HLRs and the evolutionary nature of the new numbers being added as the number of subscribers increase.
In the case where several networks have agreed to allow SMS to be sent from one network to an other; each need to send update to all its interworking partners whenever he adds a new HLR level, otherwise the other partners could not send SMS to the subscribers which have been added. An alternative is also to set a Common National Gateway which will have all the updates.
In any case, the initial set-up of a large number of HLR levels, and their maintenance, would require a large human administration if it was not performed automatically as the present invention does.